This invention relates to long life motor driven pump systems, and particularly pump systems of the type that employ the same liquid that is being pumped as lubricant within the motor housing, even though the liquid in the pump can vary widely in temperature and viscosity.
Motor driven pump systems in which the rotor is enclosed within a liquid filled shell are known and are used in a number of applications. A significant advance in such systems has been provided by the teachings of U.S. Pat. No. 6,068,455, to Kenneth W. Cowans, issued May 30, 2000 and entitled xe2x80x9cLong Life Pump Systemxe2x80x9d. This type of pump system is particularly needed where the properties of the liquid being pumped may change substantially with time because of temperature and viscosity differences, as can occur in a temperature control system for semiconductor fabricating tools. Such systems must reliably operate over exceptionally long life spans in order that the expensive fabricating tools with which they are used need not be shut down periodically for pump or motor servicing. The system of the ""455 patent teaches how the same thermal transfer fluid that is being pumped can be within the interior of the closed rotor housing, and lubricate hydrodynamic bearings in an essentially athermal manner, regardless of the temperature and viscosity variations of the same fluid at the pump. The rotor interior is isolated from thermal variations in the pump to a sufficient degree by restricting interflow, and by limited heat conduction and convection paths.
Manufacturing costs and assembly techniques, however, are always of importance in units of this kind, particularly where volume production rates are required. Thus it can be very useful for the pump/rotor system to be so designed as to be externally fillable and made of interchangeable parts that can be readily assembled, but at the same time remain leak free for long periods when in service. Finding other means of cost reduction, as by simplification and standardization of parts, are other paramount objectives. Further, it is desirable to have greater versatility in system operation, such as the ability to vary the pump rate with minimal changes of components. In addition the unit should be compact and operate stably with minimal wear of the moving parts during its service life. These and other objectives are achieved, in accordance with the invention, by the novel configuration disclosed herein.
A regenerative turbine-type pump operated by an adjacent motor having a fluid-filled enclosed rotor disposes the rotor within a nonmagnetic cylindrical shell completed at each end by closure members which can provide bearing surfaces for a central shaft. One end of the shaft extends into the interior of the pump housing, to provide a rotatable mount for at least one impeller. The pump housing is secured to a motor housing, which itself encompasses the stator provided about the cylindrical shell. Thermal conductivity between the pump and motor is low because the units are designed to have minimal areal contact between abutting metal parts of relatively low conductivity. Alternatively, a low thermal conductivity element concentric with the shaft can be interposed between the two housings. The end structure for one end of the cylindrical shell comprises an end hub having a central bore open to the interior of the rotor shell, the end hub being maintained in position by a removable end cap for the motor housing. An interposed concentric compression spring about the central bore holds the end hub tightly against the end hub when the housing end cap is tightened in place, even though the end hub is not physically joined to the shell. The central bore in the end hub is closed by a closure member for the rotor shell which seats a fill valve for the thermal transfer fluid. Short central bores in the shaft from each end, with radial outlets into the rotor interior enable thermal transfer fluid to flow into the inner side of the bearings at each end of the rotor. After filling, the fluid volume within the rotor and about the hydrodynamic bearings stabilizes in temperature and is not destabilized in by immaterial amounts of fluid movement.
This arrangement provides a simplified shell construction about the rotor that is effectively scaled against leakage for long use periods. Nonetheless, it can be assembled and disassembled with replacement parts, because the concentric compression spring compensates for tolerance variations between parts. The spring, such as a Belleville spring, exerts a selected substantial compressive force along the central axis to maintain the rotor enclosure sealed after assembly. The end supports adjoining or coupled to the rotor shell usefully form journals for the shaft ends when surfaced with a noble metal, such as silver. Alternatively, integral hydrodynamic bearings for long life operation can be supported by sleeves inserted within the rotor shell as journals for bearings at each end of the shaft, and to account for size differences between the end supports and the rotor shaft.
Another useful aspect of the invention derives from limited heat conductive paths existing between the pump housing and the rotor enclosure provided by spaced apart legs on the pump housing engaging the motor housing and an inner ring engaging the rotor shell or an intervening isolator. Other alternative features of the construction include the inclusion of an integral rotor shell and end sleeve on the pump side, and a single end closure member on the fill side, reducing both the number of parts employed and the cost.
In accordance with another feature of the invention, the pump housing may be configured to receive an extended end on the rotor shaft, which end includes two axially spaced apart mounting surfaces for attachment of one or, alternatively, two impellers. Also, the impeller housing is configured with a base on the rotor side and an opposed end cap which can either be directly coupled to the base or to an interposed spacer element which mates between the base and end cap. When the insert and second impeller are included in the pump housing the flow paths for the thermal transfer fluid are still maintained in continuity between the inlet and outlet.